The present invention is directed to patterning material so as to form electronic circuitry components, particularly from thin film materials, such as those which can be deposited by combustion chemical vapor deposition (CCVD) and controlled atmosphere combustion chemical vapor deposition (CACCVD).
Most printed circuitry is produced these days by photoimaging processes. In a typical process, the starting material is a blank comprising a dielectric material, such as a fiberglass/epoxy composite, on which is provided a layer of metal, such as copper. The copper is covered with a photoresist. The photoresist is exposed through artwork to actinic radiation. The unexposed portions of the photoresist are developed away (in a negative acting photoresist). Then, the exposed copper is etched away. Finally, the remaining photoimageable composition is stripped.
While resolution through photoimaging processes is continually improving, there remains a need for enhanced resolution. At the same time, photoimaging techniques have inherent resolution limitations. Resolution is limited by the thickness of the metal layer on the blank because chemical etching proceeds sideways as well as through the copper layer. Resolution is also limited by the thickness of the photoresist layer, which in turn is limited by physical parameters. Thus, it is an object of the present invention to provide a process of patterning printed circuitry components, such as circuitry traces, resistors, and capacitor plates with a resolution finer than that of the inherent limitations of photoimaging processes.
U.S. Pat. No. 5,652,021 and U.S. patent application Ser. No. 08/691,853, filed Aug. 2, 1996, the teachings of each of which are incorporated by reference, describe CCVD processes which are useful for depositing a number of metal and metalloid oxides, such as silica, as well as certain zero valence metals, such as platinum. To deposit more reactive metals in zero valence states, such as zinc, nickel, copper, etc. oxidation of the metal must be prevented. To this end, U.S. Pat. No. 09/067,975, the teachings of which are incorporated herein by reference, describe controlled atmosphere combustion chemical vapor deposition (CACCVD) where the amount of oxygen used in the combustion is sufficiently controlled that a variety of zero valence metals, such as zinc, can be deposited. Both CCVD and CACCVD provide for the depositions of very thin, i.e., as thin as 25 nm, continuous, integral films of a variety of materials. Though the present invention does not require that deposited layers described herein be deposited by CCVD and/or CACCVD, these currently represent the best mode known to the inventor of depositing such thin layers, particularly on a large scale such as would be require for production runs.
U.S. patent application Ser. No. 09/198,954, the teachings of which are incorporated herein by reference, teaches the formation of thin film resistors from thin films deposited by CCVD.
In accordance with one aspect of the invention, there is provided a dielectric material substrate and a thin layer of conductive material deposited thereon, the conductive material having a boiling temperature and the substrate having a melting point or decomposition temperature above that of the boiling point of the conductive material. The conductive material is patterned with computer guided laser which provides sufficient thermal energy to selected portions of the conductive material layer to boil off those portions of the conductive material layer without decomposing or melting the substrate.
In accordance with one preferred aspect of the invention, a three-layer structure is provided comprising a metal foil layer, a thin dielectric material layer, and a conductive material layer. The conductive material layer has a boiling point which is substantially below the melting point or decomposition temperature of the dielectric material and below the melting point of the foil layer. Again, the conductive material is patterned with computer guided laser which provides thermal energy to selected portions of the conductive material layer to boil off those portions of the conductive material layer without decomposing or melting the substrate. One combination of material for such a substrate comprises a nickel foil layer; a metal or metalloid oxide layer, such as silica; and a zinc conductive layer.
In accordance with another aspect of the invention, it is found that a layer of material between about 0.05 and about 3 microns thick on a dissimilar material substrate may be ablated away in a predetermined pattern by thermal energy provided by a computer guided laser. In particular, a conductive material between about 0.05 and about 3 microns thick can be patterned by computer guided laser.
One application for such an ablative process is a thin platinum layer on a substrate of a dissimilar metal, such as copper foil. As described in above-referenced U.S. patent application Ser. No. 09/198,954, the platinum may be doped with a dielectric material, such as silica, such that patches of the platinum layer may be patterned to provide electrical resistor elements. Portions of the platinum layer, when exposed to thermal energy provided by a computer-guided laser, ablate away from the copper foil substrate.